In the automotive industry it is often necessary to seal gaps and joints in metal structures using an adhesive plug or patch. For example, where a stamping and a structural beam meet a longitudinal gap may arise. In addition, drainage holes, assembly access holes, fastening holes, tooling holes, weld access holes and the like are often formed in automobile body structures and must be subsequently closed. As will be appreciated by those skilled in the art, if left unsealed these gaps and holes allow dust and fumes to enter the passenger compartment and create a source for water leakage and corrosion.
A number of devices have been used in the past to seal gaps and holes in automotive bodies. Assemblies of hot melt adhesives have been clipped into place on the unsealed hole such that the adhesive melts as the vehicle passes through a paint oven. Resilient rubber plugs have been forced by hand into access holes to create a seal. Both of theses techniques, however, usually require the use of considerable mechanical force by the assembly technician which is undesirable. Moreover, if improperly placed these devices may become loose or even dislodge during movement of the vehicle down the assembly line. Also, metal clips in contact with the vehicle body may create a source of metal corrosion (owing to galvanic corrosive activity).
In order to facilitate the closure of longitudinal gaps between parts, hot melt adhesive tapes were developed which could be rolled out to the desired length and placed over the gap. In many instances there was sufficient tack to the tape to hold it in place until the vehicle passed through an oven whereupon the adhesive melted and flowed into the gap, effectively forming a seal. In some applications, however, a technique was needed to hold the tape in position until the adhesive could be melted.
In response to this need for a method of retaining the tape in position (for example where the gap to be sealed faced downwardly), a self-adhering magnetic tape was developed. These prior art magnetized hot melt adhesive tapes comprise long, thin ribbons of thermoset or thermoplastic resins admixed with magnetizable particles. More specifically, many of these prior art magnetic tapes are formed by blending a thermoplastic resin, various elastomers and tackifiers, and magnetizable particles such as barium ferrite to form an extrudable polymer mixture. The mixture is then extruded to form a relatively thin, planar ribbon or tape. After the tape has cooled the ferrite particles are magnetized by passing the tape through a magnetizer.
In use, these prior art magnetic tapes are placed on the ferrometallic parts along the gap. The magnetic field generated by the magnetized particles is sufficient to temporarily bond the tape to the adjacent metal. As the resin components of the tape begin to melt, it is claimed that there is sufficient magnetic force to draw the tape into the gap to form a complete seal. Following the melt phase, the magnetic tape is usually at least partially demagnetized, but the adhesive properties of the tape continue to form a strong bond with the metal surfaces.
Prior art magnetic tapes are exemplified in a number of prior art patents. For example U.S. Pat. No. 4,427,481 discloses a magnetic hot melt adhesive which is extruded to form a tape. It is stated therein that the extrusion die can be altered to produce a magnetized adhesive of triangular or circular cross-section. U.S. Pat. No. 4,769,166 describes an expandable magnetic sealant which is first formed as a tape and is then cut to a desired length or shape. U.S. Pat. Nos. 4,724,243 and 4,749,434 similarly disclose hot melt magnetic sealants.
While these prior art tapes are useful in many applications, the geometry of tapes, cylinders and triangles are often incompatible with the space to be sealed. This lack of conformity in the geometries of the magnetic adhesive and the hole or gap may result in only partial closure of the space or insufficient contact between the magnetized body and the ferrometallic structure. As a result the initial adhesive and magnetic bond may not hold the tape in place. It will be appreciated by those skilled in the art that if a hot melt adhesive patch is dislodged and then melts at an arbitrary position in the vehicle, in many instances it must be subsequently removed. Therefore, it would be desirable to provide a hot melt patch adhesive which is well secured to the metallic surface prior to the melt phase of the process.
In addition, in some applications the hot melt adhesive does not provide sufficient strength at the sealed gap. For example the present inventor has found that conventional hot melt patches rupture under relatively modest loads. Therefore, it would be desirable to provide a hot melt patch which has high physical strength to resist rupture.